1. Area of the Art
The invention relates generally to methods of rinsing and drying wafers in semiconductor processing, and specifically to methods of drying wafers using hot deionized (DI) water in conjunction with infrared (IR) drying techniques.
2. Description of the Prior Art
The manufacture of semiconductor wafers used for device manufacturing requires several mechanical and/or chemical processes, typically followed by chemical cleaning of the wafers to remove particle contaminants from the wafer surface. Both particle size (measured in micrometers) and particle frequency are measured, with technology continually striving to reduce both size and frequency. The present state of the art calls for a combination of chemicals and ultrasonic or megasonic energy to remove the particles.
Upon completion of the cleaning step, the wafers must be dried. One common method employs a spin dryer. These dryers are basically centrifuges that throw water from both the wafers and cassettes that contain them. This method of drying induces a high stress on the wafers, which can lead to structural failure of the wafer. It can also deposit small particles on the wafer generated by the motion of the dryer.
Another common method of drying wafers is solvent vapor drying, with isopropyl alcohol (IPA) being the typical solvent used. This method improves upon the spin drying method by eliminating the high stress induced by the centrifuge, and produces a more particle-free wafer, providing a high quality solvent is used. However, this method produces other drawbacks. Most notably, copious quantities of solvent are required, and disposing of the solvent waste is both expensive and detrimental to the environment. Further, the handling mechanisms and the deionized (DI) water quality used in the cleaning system must be maintained with extreme fastidiousness. Any contaminations in the water or on the handling mechanisms are readily transferred to the wafers and distributed across the wafer surface by the solvent.
A relatively new technique is capillary drying, requiring only hot DI water. The wafers are extracted out of a hot DI water bath at a slow rate. For optimal particle control, current art such as U.S. Pat. No. 4,902,350 suggests that water temperature should be between 80.degree. and 85.degree. C., with the wafers being extracted from the DI bath at a pull rate of between 2.5 and 10 centimeters per minute.
Another relatively new technique uses infrared (IR) drying. This technique typically employs a medium-wavelength IR (wavelength of approximately 2.6 microns) heater and a short-wavelength IR (wavelength approximately 1.2 microns) heater for drying the surfaces of the wafer. The short-wavelength IR heater must be aimed directly at the surface of the wafer, and therefore can only dry one wafer at a time. Thus, productivity is severely limited.